HTTP authentication with PHP
It is possible to use the header() function to send an "Authentication Required" message to the client browser causing it to pop up a Username/Password input window. Once the user has filled in a username and a password, the URL containing the PHP script will be called again with the predefined variables PHP_AUTH_USER, PHP_AUTH_PW, and AUTH_TYPE set to the user name, password and authentication type respectively. These predefined variables are found in the $_SERVER and $HTTP_SERVER_VARS arrays. Both "Basic" and "Digest" (since PHP 5.1.0) authentication methods are supported. See the header() function for more information.
Note: PHP Version Note
An example script fragment which would force client authentication on a page is as follows:
Example #6 Basic HTTP Authentication example
<?phpif (!isset($_SERVER['PHP_AUTH_USER'])) {
header('WWW-Authenticate: Basic realm="My Realm"');
header('HTTP/1.0 401 Unauthorized');
echo 'Text to send if user hits Cancel button';
exit;
} else {
echo "<p>Hello {$_SERVER['PHP_AUTH_USER']}.</p>";
echo "<p>You entered {$_SERVER['PHP_AUTH_PW']} as your password.</p>";
}?> Example #7 Digest HTTP Authentication example
This example shows you how to implement a simple Digest HTTP authentication script. For more information read the » RFC 2617.
<?php
$realm = 'Restricted area';
//user => password$users = array('admin' => 'mypass', 'guest' => 'guest');
if (empty($_SERVER['PHP_AUTH_DIGEST'])) {
header('HTTP/1.1 401 Unauthorized');
header('WWW-Authenticate: Digest realm="'.$realm.
'",qop="auth",nonce="'.uniqid().'",opaque="'.md5($realm).'"');
die('Text to send if user hits Cancel button');
}
// analyze the PHP_AUTH_DIGEST variableif (!($data = http_digest_parse($_SERVER['PHP_AUTH_DIGEST'])) ||
!isset($users[$data['username']]))
die('Wrong Credentials!');
// generate the valid response$A1 = md5($data['username'] . ':' . $realm . ':' . $users[$data['username']]);$A2 = md5($_SERVER['REQUEST_METHOD'].':'.$data['uri']);$valid_response = md5($A1.':'.$data['nonce'].':'.$data['nc'].':'.$data['cnonce'].':'.$data['qop'].':'.$A2);
if ($data['response'] != $valid_response)
die('Wrong Credentials!');
// ok, valid username & passwordecho 'Your are logged in as: ' . $data['username'];
// function to parse the http auth headerfunction http_digest_parse($txt)
{
// protect against missing data
$needed_parts = array('nonce'=>1, 'nc'=>1, 'cnonce'=>1, 'qop'=>1, 'username'=>1, 'uri'=>1, 'response'=>1);
$data = array();
$keys = implode('|', array_keys($needed_parts));
preg_match_all('@(' . $keys . ')=(?:([\'"])([^\2]+?)\2|([^\s,]+))@', $txt, $matches, PREG_SET_ORDER);
foreach ($matches as $m) {
$data[$m[1]] = $m[3] ? $m[3] : $m[4];
unset($needed_parts[$m[1]]);
}
return $needed_parts ? false : $data;
}?> Note: Compatibility Note
Please be careful when coding the HTTP header lines. In order to guarantee maximum compatibility with all clients, the keyword "Basic" should be written with an uppercase "B", the realm string must be enclosed in double (not single) quotes, and exactly one space should precede the 401 code in the HTTP/1.0 401 header line. Authentication parameters have to be comma-separated as seen in the digest example above.
Instead of simply printing out PHP_AUTH_USER and PHP_AUTH_PW, as done in the above example, you may want to check the username and password for validity. Perhaps by sending a query to a database, or by looking up the user in a dbm file.
Watch out for buggy Internet Explorer browsers out there. They seem very picky about the order of the headers. Sending the WWW-Authenticate header before the HTTP/1.0 401 header seems to do the trick for now.
As of PHP 4.3.0, in order to prevent someone from writing a script which reveals the password for a page that was authenticated through a traditional external mechanism, the PHP_AUTH variables will not be set if external authentication is enabled for that particular page and safe mode is enabled. Regardless, REMOTE_USER can be used to identify the externally-authenticated user. So, you can use $_SERVER['REMOTE_USER'].
Note: Configuration Note
PHP uses the presence of an AuthType directive to determine whether external authentication is in effect.
Note, however, that the above does not prevent someone who controls a non-authenticated URL from stealing passwords from authenticated URLs on the same server.
Both Netscape Navigator and Internet Explorer will clear the local browser window's authentication cache for the realm upon receiving a server response of 401. This can effectively "log out" a user, forcing them to re-enter their username and password. Some people use this to "time out" logins, or provide a "log-out" button.
Example #8 HTTP Authentication example forcing a new name/password
<?phpfunction authenticate() {
header('WWW-Authenticate: Basic realm="Test Authentication System"');
header('HTTP/1.0 401 Unauthorized');
echo "You must enter a valid login ID and password to access this resource\n";
exit;
}
if (!isset($_SERVER['PHP_AUTH_USER']) ||
($_POST['SeenBefore'] == 1 && $_POST['OldAuth'] == $_SERVER['PHP_AUTH_USER'])) {
authenticate();
} else {
echo "<p>Welcome: " . htmlspecialchars($_SERVER['PHP_AUTH_USER']) . "<br />";
echo "Old: " . htmlspecialchars($_REQUEST['OldAuth']);
echo "<form action='' method='post'>\n";
echo "<input type='hidden' name='SeenBefore' value='1' />\n";
echo "<input type='hidden' name='OldAuth' value=\"" . htmlspecialchars($_SERVER['PHP_AUTH_USER']) . "\" />\n";
echo "<input type='submit' value='Re Authenticate' />\n";
echo "</form></p>\n";
}?> This behavior is not required by the HTTP Basic authentication standard, so you should never depend on this. Testing with Lynx has shown that Lynx does not clear the authentication credentials with a 401 server response, so pressing back and then forward again will open the resource as long as the credential requirements haven't changed. The user can press the '_' key to clear their authentication information, however.
Also note that until PHP 4.3.3, HTTP Authentication did not work using Microsoft's IIS server with the CGI version of PHP due to a limitation of IIS. In order to get it to work in PHP 4.3.3+, you must edit your IIS configuration "Directory Security". Click on "Edit" and only check "Anonymous Access", all other fields should be left unchecked.
Another limitation is if you're using the IIS module (ISAPI) and PHP 4, you may not use the PHP_AUTH_* variables but instead, the variable HTTP_AUTHORIZATION is available. For example, consider the following code: list($user, $pw) = explode(':', base64_decode(substr($_SERVER['HTTP_AUTHORIZATION'], 6)));
Note: IIS Note:
For HTTP Authentication to work with IIS, the PHP directive cgi.rfc2616_headers must be set to 0 (the default value).
Note:
If safe mode is enabled, the uid of the script is added to the realm part of the WWW-Authenticate header.
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Last updated: Fri, 17 Jun 2011
Features Last updated: Fri, 17 Jun 2011
add a note User Contributed Notes HTTP authentication with PHP Anonymous 06-Mar-2011 02:22
Quickly and without combining, for example, we do a new folder LOGOUT and throw to him .htaccess files with some virtual user:
AuthName "protected area"
Access allow all users Logout
set the error page 401
ErrorDoc 401 "protected area"
and set a link to our new folder <a href="./logout/">logout</ a>
... when I click on enter into a virtual folder with a security dialog to confirm the login without supplying a user name and password and are logged off. Works on FF, IE, Opera ... ceo at l-i-e dot com 13-Oct-2010 10:51
To force a logout with Basic Auth, you can change the Realm out from under them to a different Realm.
This forces a new set of credentials for a new "Realm" on your server.
You just need to track the Realm name with the user/pass and change it around to something new/random as they log in and out.
I believe that this is the only 100% guaranteed way to get a logout in HTTP Basic Auth, and if it were part of the docs a whole lot of BAD user-contributed comments here could be deleted. Ollie L 24-Sep-2010 11:16
I tried example 7, and at first I couldn't get it to work. It took me a while to spot that somewhere along the line, probably by the server, a seemingly random number was being added to the realm - so the valid_result variable wasn't calculated using the correct realm.
To get around this, or any similar problems, make the following changes to the example:
Around line 43 (44 if after next step ;) ):
$needed_parts = array('nonce'=>1, 'nc'=>1, 'cnonce'=>1, 'qop'=>1, 'username'=>1, 'uri'=>1, 'response'=>1, 'realm'=>1);
Before line 24:
$realm = $data['realm'];
These two steps get the real realm used for the authentication request, and substitute it into the "valid_response" query.
Hope this helps :) 
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